In this study, I hoped to determine the extent that fertilizer runoff causes eutrophication in Prisoner’s Pond (Caldwell, NJ, USA). Measuring dissolved oxygen levels with the Vernier LabQuest Probe and comparing the data to precipitation levels, I found enough correlation between high dissolved oxygen during periods of low precipitation and vice versa to tentatively determine causation.
Prisoner’s Pond is located on a border between protected, untouched forest reservation and Caldwell, a densely populated town of around 8,000 in Essex County, according to the 2019 census. The Pond’s position directly downhill from a housing community aroused questions surrounding nutrient runoff and eutrophication. Upon further in-person observation and online research, I found that the pond experienced bouts of severe algal bloom, in which most of the pond’s surface was completely covered in a thick layer of algae. The severe anthropogenic changes in land use and prevalence of impervious surfaces encouraged me to examine the prospect of runoff-based eutrophication. I endeavored to determine whether fertilizer runoff from the housing community uphill was a significant factor. In the course of my study, I also found evidence of a direct drain system from roadside drains into Prisoner’s Pond.
Eutrophication is a common environmental concern in many urban ecosystems. Often in urban or dense suburban areas, intense bouts of rain cause fertilizer runoff from developments and result in eutrophication in the form of algal bloom. The role of impervious surface (roads, pavement, etc.) cannot be understated; rather than allow runoff to infiltrate into groundwater stores, impervious surface forces more volume of water to flow into lower elevation water bodies. The resulting flow of excess nitrogen and phosphorus allows the algae to grow unfettered since the once-limiting nutrients are now present in high quantities. The effect is two-fold; the great volume of algae blocks out other organisms like duck leaf. Furthermore, great amounts of algae die at the same time after the bloom, resulting in an unusually large share of oxygen consumption by bacterial decomposers, which feed on the remains of the dead algae. These decomposers are the culprit for acute drops in the pond’s dissolved oxygen level. If the dissolved oxygen level drops too low, fish and other oxygen-dependent organisms will die out. These low-species and oxygen-depleted areas are called dead zones.
To ascertain if this series of events was taking place at Prisoner's Pond, I measured dissolved oxygen levels over four months between January and April. I compared it with trends in precipitation data over the same period. Using the Vernier GoDirect Optical Dissolved Oxygen sensor connected to my cellular device via Bluetooth, I was able to measure dissolved oxygen at Prisoner’s pond regularly over this period. I also downloaded precipitation data from Teterboro Airport, which is the closest official weather station to the pond. I hypothesized that periods of high rainfall would cause lower dissolved oxygen and periods of low rainfall would cause higher dissolved oxygen.
My data supported this thesis, showing that bouts of rainfall were indeed followed by periods of lower dissolved oxygen, and vice versa. From March 25, 2021, to April 2, 2021, the pond experience more than two inches of rain. Consequently, dissolved oxygen levels fluctuated between 8.33 mg/L and 10.23 mg/L. However, during the period between April 3, 2021, and April 11, 2021, in which the pond received no precipitation, dissolved oxygen increased significantly, hovering between 10.23 mg/L and 12.06 mg/L. Similar trends were observed throughout the data collection period–this example was the most extreme.
Based on these data, I was able to conclude that fertilizer runoff from the development above may contribute to eutrophication. While the data were promising, without actually testing the water for the fertilizers used for lawns, I can only tentatively make this conclusion. Though my work has contributed evidence towards the hypothesis that surface runoff is the source of algal bloom, important steps are yet to be taken to truly pinpoint the source of eutrophication. Take the pipe I identified: it could run from a different source altogether. To further advance my findings, I would test more specifically for common lawn fertilizers in Prisoner’s pond and cross-reference these chemicals with those used on the housing development uphill. I would also measure nitrogen and phosphorous levels directly to further cement the correlation I viewed with dissolved oxygen. While the dissolved oxygen correlation implies elevated nitrogen and phosphorous level, this extra step would ensure the relationship between runoff and algal bloom.
Over four months of collecting data on dissolved oxygen and precipitation at Prisoner’s Pond, I found data that suggests a correlation between nutrient runoff and algal bloom. My findings show promising results, and with further study in specific anthropogenic regions in the proximity of the pond, may conclusively point to fertilizer runoff from housing developments uphill as a direct cause of eutrophication in Prisoner’s Pond.